As Flight Lieutenant George McInnes flew over the Pike River mine site yesterday his thoughts were with his best friend Michael Monk, one of 29 miners whose bodies remain entombed inside.

A Defence Force helicopter has removed 25 tonnes of debris from the Pike River mine - the first step to recovering the bodies.

Work began yesterday removing material from the top of the West Coast mine in preparation for an attempt to re-enter the mine.

The New Zealand Defence Force (NZDF) is providing assistance to Solid Energy, using a helicopter to hoist material from the top of the mine's ventilation shaft to clear the area for stage one of the project.

Flight Lieutenant McInnes requested to be part of the operation.

"I have to admit I was thinking of Michael and his family, but I had to push those thoughts to the back of my mind because we had an important job to do,'' he said.

The pair forged a strong friendship at boarding school in Christchurch where they attended St Bede's College and on leaving school they completed a gap year in Ireland together coaching rugby, he said.

"When we came back to New Zealand Michael took up a builder's apprenticeship on the coast and soon after I joined the Air Force.''

Flight Lieutenant McInnes is one of three three NH90 helicopter co-pilots assisting with the removal of material from around the top of the main ventilation shaft.

"It's pretty special for me to be able to help out and it was really good to catch up with Michael's parents Bernie and Kath Monk.

"We are certainly learning a lot while we are down here, it's challenging work with underslung loads but the NH90s are proving to be very effective with the task.''

Bernie Monk said his son and Flight Lieutenant McInnes were very close friends and it was emotional to have him there.

"His mother rang us last night and said that George was one of the four pilots that were working at the Pike River job and it was quite moving, for my wife especially,'' he said.

"They had been together at St Bede's for five years and they were also tutors in Ireland together for a year where they became good friends. so it was nice to have him on board.''

The work began nearly nearly three years after 29 men died in the mine during a series of explosions.

"The Government has been working closely with Solid Energy to ensure the re-entry plan can be safely carried out. Safety is paramount, and the project will be carefully managed with a risk assessment undertaken at each stage," Mr Bridges said.

The Air Force NH90 helicopter is supported by a team of NZ Army air lift operations personnel.

"This is the first time an Air Force NH90 helicopter has been tasked to support another government agency in this type of operation," Dr Coleman said.

Good weather this morning meant the team was able to make an early start, already lifting away 25 tonnes of debris.

Up to 20 loads are expected to be transported this week.

"The NH90 has twice the lifting capacity of civilian helicopters. It is an advanced medium utility helicopter with state-of-the-art technology, and the capability allows the Defence Force to undertake a wide variety of roles."

However, the operation didn't include entry into the main mine, which was blocked by the rock fall, Mr Bridges said.

"The Government cannot speculate on re-entering the main mine until the tunnel re-entry has been successfully achieved."

It is understood the operation could take up to six months to recover the sons, husbands, partners and fathers trapped underground. While families of the victims are excited the day has finally arrived, most believe work should have begun about two and a half years ago.

Early last month Prime Minister John Key pledged $10 million of government support for a re-entry plan if it was safe, technically feasible and financially credible.

The staged re-entry plan is designed to seal off the ventilation shaft in the mine's main entry tunnel, known as the drift.

The mine will be pumped full of nitrogen to force out any methane gas and allow experts to walk down a 2.3km shaft to a rockfall.

While most of the bodies were believed to be inside the mine's main workings, the families believe some men may have been inside the drift when blasts ripped through the mine on November 19, 2010.

The military hopes to finish the clearing stage above the ventilation shaft this week.

Acting commanding officer of the helicopter transition unit Anna Shaw said they would "stay here till we have got the job done''.